CN116083892A - A kind of non-phosphorus and nitrogen-free conversion agent before painting and preparation method thereof - Google Patents

Abstract

The invention relates to the technical field of chemical materials, in particular to the field of IPC C23C22, and more particularly relates to a phosphorus-free and nitrogen-free conversion agent before coating and a preparation method thereof. The invention prepares a phosphorus-free nitrogen-free conversion agent before coating by 3 to 15 percent of fluoride ion compound, 0.02 to 1 percent of nano dispersion liquid, 0.01 to 1 percent of low carbon alcohol, 1 to 5 percent of silane coupling agent, 0.1 to 2 percent of nitrogen-free oxidant, 0.01 to 0.5 percent of zirconium sol, 0.01 to 0.5 percent of titanium sol, 0.1 to 0.5 percent of complexing agent, 0.15 to 0.3 percent of rare earth compound and deionized water. The pre-coating conversion agent is safe and environment-friendly, and is uniform in film formation, high in conversion speed and good in rust resistance.

Description

A phosphorus-free and nitrogen-free pre-coating conversion agent and preparation method thereof

Technical Field

The present invention relates to the technical field of chemical materials, in particular to the field of IPC C23C22, and more specifically to a phosphorus-free and nitrogen-free pre-coating conversion agent and a preparation method thereof.

Background Art

Ceramic treatment (including silane composite ceramic treatment) is a metal surface coating pretreatment method that replaces traditional phosphating. It generally refers to the process of contacting the metal surface with an acidic solution containing fluorine zirconate/titanate, utilizing the hydrolysis process of fluorine zirconate/titanate to form a stable, insoluble inorganic compound film on the metal surface through chemical and electrochemical reactions. A layer of zirconium-titanium film can be formed by ceramic silane treatment on the metal surface. This film can provide a certain degree of corrosion protection for the substrate, while also ensuring excellent bonding with the subsequent coating process, and together with the coating, provide the substrate with excellent anti-corrosion performance.

Existing patent CN200610141044.1 discloses a composition for surface treatment of light metals and their composite materials. The composition contains water-soluble metavanadate, water-soluble phosphorus-containing compounds and water-soluble rare earth salts, which can improve the corrosion resistance of the rare earth conversion film and the adhesion of the paint film. However, the composition contains a large amount of phosphates, which will cause greater environmental pollution.

The existing patent CN201711102545.3 discloses a nano-complex synthetic film agent, the main components of which are film-forming agent, silane coupling agent, sealing agent, film-forming aid, oxidant, complexing agent, and sustained-release agent. It can improve the corrosion resistance of the material, but some of them contain ammonium salts, alcohol amines and other ingredients, which will cause certain environmental pollution.

In the pre-ceramic treatment process, degreasing and washing, especially in the transition stage between washing and ceramic treatment, since the clean steel surface is very easy to be oxidized to form rust, rust inhibitors are usually used in the washing liquid. Currently, the available rust inhibitors basically contain nitrogen, including: sodium nitrite, alcohol amine, salts or esters containing alcohol amine. Both ammonia nitrogen and nitrate nitrogen are the main pollution factors of environmental eutrophication and need to be restricted.

There is currently only a small amount of research in the industry on this application demand. The phosphorus-free and nitrogen-free silane zirconization products that have been launched on the market have problems such as long processing time, thin zirconization film, uneven film formation, poor stability, and poor corrosion resistance. For some customers with slightly higher requirements, it is difficult to meet the quality requirements.

Summary of the invention

In order to overcome the shortcomings of the prior art, the first aspect of the present invention provides a phosphorus-free and nitrogen-free pre-coating conversion agent, the raw materials for its preparation, by mass percentage, are 3-15% fluoride ion compound, 0.02-1% nano-dispersion liquid, 0.01-1% low-carbon alcohol, 1-5% silane coupling agent, 0.1-2% nitrogen-free oxidant, 0.01-0.5% zirconium sol, 0.01-0.5% titanium sol, 0.1-0.5% complexing agent, 0.15-0.3% rare earth compound, and the balance is deionized water.

Preferably, the fluoride ion compound comprises one or more of fluorozirconic acid, fluorotitanic acid, potassium fluorozirconate, potassium fluorotitanate, sodium fluorozirconate, and sodium fluorotitanate.

Preferably, the nano-dispersion liquid includes one or more of γ-phase alumina, fumed silica, nano-barium sulfate, and nano-calcium carbonate; more preferably, it is γ-phase alumina and fumed silica.

Preferably, the mass ratio of the γ-phase alumina to the fumed silica is (1-3):1; more preferably, it is 1:1.

Preferably, the average particle size of the γ-phase alumina is 20 nm.

Preferably, the γ-phase alumina is purchased from Xuancheng Jingrui New Materials Co., Ltd., model number VK-L20W.

Preferably, the fumed silica is hydrophilic fumed silica.

Preferably, the hydrophilic fumed silica is purchased from Hubei Huifu Nanomaterials Co., Ltd., model HL-300.

In the present invention, 0.02-1% of nano-dispersed liquid is added to improve the mechanical properties of the conversion film, and at the same time, an organic complex salt is formed with other substances in the system, which can effectively alleviate the penetration of water, oxygen, chloride ions, etc. into the interior of the object. The inventor creatively discovered that in the process of forming the conversion film, the addition of the nano-dispersed liquid accelerates the formation speed of the conversion film, and at the same time increases the density of the conversion film, thereby enhancing its adhesion and rust resistance. Too much content of the nano-dispersed liquid will reduce the adhesion and solution stability, resulting in unstable formation of the conversion film, and weakening the rust and corrosion resistance effects.

Preferably, the low-carbon alcohol includes one or more of methanol, ethanol, and isopropanol; more preferably, it is isopropanol.

Preferably, the silane coupling agent includes one or more of γ-(2,3-epoxypropoxy)propyltrimethoxysilane, epoxysilane oligomer, 1,2-bis(triethoxysilyl)ethane, 3-chloropropyltriethoxysilane, 3-mercaptopropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, and vinyltrimethoxysilane; further preferably, it is one or more of γ-(2,3-epoxypropoxy)propyltrimethoxysilane, epoxysilane oligomer, 3-chloropropyltriethoxysilane, and γ-methacryloxypropyltrimethoxysilane.

Preferably, the γ-(2,3-epoxypropoxy)propyltrimethoxysilane is purchased from Jiangsu Rayen Environmental Protection Technology Co., Ltd.

Preferably, the epoxysilane oligomer is purchased from Guangzhou Zhongjie New Materials Co., Ltd., model number 8066.

Preferably, the 3-chloropropyltriethoxysilane is purchased from Jiangsu Runfeng Synthetic Technology Co., Ltd.

Preferably, the γ-methacryloxypropyltrimethoxysilane is purchased from Hubei Jianghan New Materials Co., Ltd., model number JH-0174.

Preferably, the mass ratio of the fluoride ion compound to the silane coupling agent is (3-5):1; more preferably, it is 4:1.

In the present invention, by adding a fluorine ion compound and a silane coupling agent in a mass ratio of (3 to 5): 1, a dense nano-scale inorganic film can be formed, while reducing the use of promoters such as nitrite, accelerating the reaction speed; while improving production efficiency, reducing environmental pollution. The present invention speculates that by adding a fluorine ion compound and a silane coupling agent in a mass ratio of (3 to 5): 1, the metal dissociates under the action of acid under an electrochemical reaction, and the hydrolyzate of the silane coupling agent rapidly adsorbs to the metal surface through the shrinkage reaction between the SiOH group and the group on the metal surface. On the other hand, the remaining silane molecules form a silane film with a Si-O-Si three-dimensional network structure on the metal surface through a polycondensation reaction between the SiOH groups, and then act together with the nano-dispersed liquid, zirconium sol, titanium sol, complexing agent, rare earth compound and other substances in the system, and combine together through a cross-linking reaction, thereby forming a strong chemical bond, and then forming a stable film layer structure. At the same time, in this system, no nitrite promoter is used, thereby reducing environmental pollution. The reaction can also be carried out at room temperature without heating, thus reducing energy consumption.

Preferably, the nitrogen-free oxidant includes one or more of sodium molybdate, sodium tungstate, sodium chlorate, sodium bromate, and persulfate; further preferably, it is one or more of sodium chlorate and sodium bromate.

Preferably, the average particle size of the zirconium sol and titanium sol is 1 to 30 nm; more preferably, it is 5 to 20 nm.

Preferably, the average particle size of the zirconium sol is 10 nm.

Preferably, the zirconium sol is of model HN-RJ80, purchased from Hangzhou Hengge Nanotechnology Co., Ltd.

Preferably, the average particle size of the titanium sol is 10 nm.

Preferably, the titanium sol has a model of HN-TA33, purchased from Hangzhou Hengna New Materials Co., Ltd.

Preferably, the mass ratio of the silane coupling agent, zirconium sol and titanium sol is (12-18):1:1; more preferably, it is 15:1:1.

In the present invention, by adding a silane coupling agent, a zirconium sol and a titanium sol in a mass ratio of (12 to 18): 1: 1, the quality of the conversion film is improved, and the conversion treatment time is also shortened. The inventors speculate that the silane coupling agent, the zirconium sol and the titanium sol form a silane-zirconium-titanium pre-hydrolyzed copolymer, and the colloidal particles can be uniformly adsorbed on the metal surface, so that a large number of micro cathode areas are formed on the metal surface, forming crystal nuclei, eliminating the influence of the physical or chemical inhomogeneity of the metal surface state on the film formation, thereby promoting the uniform and rapid formation of crystals, preventing the growth of large crystals, making the film of the conversion film dense, and having no gaps between the films, so that it has good rust resistance and adhesion.

Preferably, the complexing agent is one or more of trisodium citrate, potassium sodium tartrate, tannic acid, sodium gluconate, lactic acid, and itaconic acid; more preferably, it is one or more of sodium citrate and potassium sodium tartrate.

In the present invention, by adding 0.1-0.5% of the complexing agent, the density of the conversion film can be improved, and the film has good rust resistance. The inventor unexpectedly found that adding 0.1-0.5% of the complexing agent can complex with the main salt to form a relatively stable metal complex ion, thereby increasing the concentration polarization and electrochemical polarization effects, controlling the deposition rate of the zirconate, and forming a dense and uniform oxide film on the metal surface, with no gaps between the films, and the film is not easy to dissolve, thereby having excellent corrosion resistance.

Preferably, the rare earth compound includes one or more of lanthanum compounds and cerium compounds; more preferably, it is lanthanum chloride.

The second aspect of the present invention provides a method for preparing a phosphorus-free and nitrogen-free pre-coating conversion agent, comprising the following steps:

S1: adding the nano-dispersant to 5% of the deionized water of the raw material, stirring and shearing at high speed at 20-25° C. for 30-120 min to obtain a nano-dispersed liquid;

S2: dissolving low-carbon alcohol into 5% deionized water of the raw material, slowly adding silane coupling agent, stirring thoroughly for 2 to 6 hours at 20 to 50° C., slowly adding zirconium sol and titanium sol, stirring evenly, and standing for 24 hours to obtain a silane-zirconium-titanium pre-hydrolyzed copolymer;

S3: Dissolve the fluoride ion compound, nitrogen-free oxidant, complexing agent and rare earth compound in the remaining amount of deionized water, add the nano-dispersion liquid and silane-zirconium-titanium pre-hydrolyzed copolymer respectively, and stir evenly.

The rotation speed of the high-speed stirring in the step S1 is 3000-5000 r/min; more preferably, it is 4000 r/min.

The third aspect of the present invention provides an application of a phosphorus-free and nitrogen-free pre-painting conversion agent, which is applied to the surface treatment of steel and aluminum alloy before painting.

Preferably, the application of the phosphorus-free and nitrogen-free pre-coating conversion agent is as follows: use it after degreasing and water washing; during the water washing process, add 0.1-2% nitrogen-free oxidant.

The necessary preparation process before the phosphorus-free and nitrogen-free conversion treatment described in the present invention, that is, in the water washing after oil removal and before the conversion treatment, 0.1-2% of nitrogen-free oxidant is added, which effectively prevents the rusting process of the metal surface and improves the anti-rust effect of the conversion film. The inventor unexpectedly found that in the water washing liquid before the conversion treatment, the effect of using halogen oxygen-containing acids such as sodium chlorate and sodium bromate is the best, and the effect of using peroxy acid salts such as persulfate is second. In this system, the use of high-valent metal salt oxidants such as molybdate and peroxides such as hydrogen peroxide is avoided. The reduction product of molybdate is a complex molybdenum heteropolyacid salt, which has a greater impact on the adhesion of the conversion film after participating in the film formation. The reduction product of hydrogen peroxide has a greater impact on the interface pH, which is easy to generate rust, which is not conducive to the phosphorus-free and nitrogen-free conversion treatment.

Beneficial Effects

1. The addition of 0.02-1% nano-dispersion improves the mechanical properties of the conversion film, and forms organic complex salts with other substances in the system, which can effectively alleviate the penetration of water, oxygen, etc. into the interior of the object.

2. By adding fluorine ion compounds and silane coupling agents in a mass ratio of (3-5):1, a dense nanoscale inorganic film can be formed, while reducing accelerators such as nitrite, accelerating the reaction rate, and reducing environmental pollution while improving production efficiency.

3. Adding 0.1-2% nitrogen-free oxidant to the washing liquid after the degreasing process and before the conversion treatment process can effectively prevent the rusting process on the metal surface. As a necessary preparatory process, it improves the anti-rust effect of the phosphorus-free and nitrogen-free conversion film.

4. By adding silane coupling agent, zirconium sol and titanium sol in a mass ratio of (12-18):1:1, the quality of the conversion film is improved and the conversion processing time is also shortened.

5. By adding 0.1-0.5% of complexing agent, the density of the conversion film can be improved and it has better rust resistance.

DETAILED DESCRIPTION

Example 1

The first aspect of the present embodiment provides a phosphorus-free and nitrogen-free pre-coating conversion agent, the raw materials for its preparation, by mass percentage, are 12% fluoride ion compound, 1% nano-dispersion liquid, 1% low-carbon alcohol, 3% silane coupling agent, 1% nitrogen-free oxidant, 0.2% zirconium sol, 0.2% titanium sol, 0.3% complexing agent, 0.2% rare earth compound, and the balance is deionized water.

The fluoride ion compound is an aqueous solution of fluorozirconic acid with a mass concentration of 45%.

The aqueous solution of fluorozirconic acid with a mass concentration of 45% was purchased from Mitsui Chemicals (Shandong) Co., Ltd.

The nano-dispersed liquid is γ-phase alumina and fumed silica.

The mass ratio of the γ-phase alumina to the fumed silica is 1:1.

The average particle size of the γ-phase alumina is 20 nm.

The γ-phase alumina was purchased from Xuancheng Jingrui New Materials Co., Ltd., model number VK-L20W.

The fumed silica is hydrophilic fumed silica.

The hydrophilic fumed silica was purchased from Hubei Huifu Nanomaterials Co., Ltd., model HL-300.

The low carbon alcohol is isopropanol.

The silane coupling agent is γ-(2,3-epoxypropoxy)propyltrimethoxysilane and epoxysilane oligomer, and the mass ratio thereof is 3:2.

The γ-(2,3-epoxypropoxy)propyltrimethoxysilane was purchased from Jiangsu Rayne Environmental Protection Technology Co., Ltd.

The epoxysilane oligomer was purchased from Guangzhou Zhongjie New Materials Co., Ltd., model number 8066.

The mass ratio of the fluoride ion compound to the silane coupling agent is 4:1.

The nitrogen-free oxidant is sodium chlorate.

The average particle size of the zirconium sol is 10 nm.

The model of the zirconium sol is HN-RJ80, which was purchased from Hangzhou Hengge Nanotechnology Co., Ltd.

The average particle size of the titanium sol is 10 nm.

The model of the titanium sol is HN-TA33, which was purchased from Hangzhou Hengna New Materials Co., Ltd.

The mass ratio of the silane coupling agent, the zirconium sol and the titanium sol is 15:1:1.

The complexing agent is sodium citrate.

The rare earth compound is lanthanum chloride.

The second aspect of this embodiment provides a method for preparing a phosphorus-free and nitrogen-free pre-coating conversion agent, comprising the following steps:

S1: Add the nano-dispersant into 5% deionized water of the raw material, stir and shear at high speed at 25°C for 120 minutes to obtain a nano-dispersed liquid;

S2: dissolving low-carbon alcohol into 5% deionized water of the raw material, slowly adding silane coupling agent, stirring thoroughly at 40°C for 6 hours, slowly adding zirconium sol and titanium sol, stirring evenly, and standing for 24 hours to obtain silane-zirconium-titanium pre-hydrolyzed copolymer;

S3: Dissolve the fluoride ion compound, nitrogen-free oxidant, complexing agent and rare earth compound in the remaining amount of deionized water, add the nano-dispersion liquid and silane-zirconium-titanium pre-hydrolyzed copolymer respectively, and stir evenly.

The rotation speed of the high-speed stirring in the step S1 is 4000 r/min.

The third aspect of this embodiment provides an application of a phosphorus-free and nitrogen-free pre-painting conversion agent, which is applied to the surface treatment of steel before painting.

The phosphorus-free and nitrogen-free pre-coating conversion agent is used in the following method: use it after degreasing and water washing; during the water washing process, add 1% nitrogen-free oxidant.

Example 2

The specific implementation method of Example 2 is the same as that of Example 1, except that, by mass percentage, it is 4% fluoride ion compound, 0.9% nano-dispersion liquid, 1% low-carbon alcohol, 1.2% silane coupling agent, 1.5% nitrogen-free oxidant, 0.1% zirconium sol, 0.1% titanium sol, 0.5% complexing agent, 0.3% rare earth compound, and the balance is deionized water.

The fluoride ion compound is fluorozirconic acid and sodium fluorozirconate, and the mass ratio thereof is 5:1.

The fluorozirconic acid is a fluorozirconic acid aqueous solution with a mass concentration of 45%.

The aqueous solution of fluorozirconic acid with a mass concentration of 45% was purchased from Mitsui Chemicals (Shandong) Co., Ltd.

The mass ratio of the γ-phase alumina to the fumed silica is 2:1.

The average particle size of the γ-phase alumina is 20 nm.

The γ-phase alumina was purchased from Xuancheng Jingrui New Materials Co., Ltd., model number VK-L20W.

The fumed silica is hydrophilic fumed silica.

The hydrophilic fumed silica was purchased from Hubei Huifu Nanomaterials Co., Ltd., model HL-300.

The low-carbon alcohol is methanol.

The silane coupling agent is 3-chloropropyltriethoxysilane.

The 3-chloropropyltriethoxysilane was purchased from Jiangsu Runfeng Synthetic Technology Co., Ltd.

The mass ratio of the fluoride ion compound to the silane coupling agent is 10:3.

The nitrogen-free oxidizing agent is sodium bromate.

The average particle size of the zirconium sol is 10 nm.

The model of the zirconium sol is HN-RJ80, which was purchased from Hangzhou Hengge Nanotechnology Co., Ltd.

The average particle size of the titanium sol is 10 nm.

The model of the titanium sol is HN-TA33, which was purchased from Hangzhou Hengna New Materials Co., Ltd.

The mass ratio of the silane coupling agent, the zirconium sol and the titanium sol is 12:1:1.

The complexing agent is potassium sodium tartrate.

The rare earth compound is lanthanum chloride.

Example 3

The specific implementation method of Example 3 is the same as that of Example 1, except that, by mass percentage, it is 10.8% fluoride ion compound, 1% nano-dispersion liquid, 0.5% low-carbon alcohol, 3.6% silane coupling agent, 0.5% nitrogen-free oxidant, 0.2% zirconium sol, 0.2% titanium sol, 0.1% complexing agent, 0.15% rare earth compound, and the balance is deionized water.

The fluoride ion compound is fluorozirconic acid, fluorotitanic acid and potassium fluorotitanate, and the mass ratio thereof is 5:4:1.

The fluorozirconic acid is a fluorozirconic acid aqueous solution with a mass concentration of 45%.

The aqueous solution of fluorozirconic acid with a mass concentration of 45% was purchased from Mitsui Chemicals (Shandong) Co., Ltd.

The fluorotitanic acid is a fluorotitanic acid aqueous solution with a mass concentration of 50%.

The aqueous solution of fluorotitanic acid with a mass concentration of 50% is from Zhonghe Chemical (Shandong) Co., Ltd.

The mass ratio of the γ-phase alumina to the fumed silica is 3:1.

The average particle size of the γ-phase alumina is 20 nm.

The γ-phase alumina was purchased from Xuancheng Jingrui New Materials Co., Ltd., model number VK-L20W.

The fumed silica is hydrophilic fumed silica.

The hydrophilic fumed silica was purchased from Hubei Huifu Nanomaterials Co., Ltd., model HL-300.

The low-carbon alcohol is ethanol.

The silane coupling agent is γ-methacryloxypropyltrimethoxysilane.

The γ-methacryloxypropyltrimethoxysilane was purchased from Hubei Jianghan New Materials Co., Ltd.

The mass ratio of the fluorine ion compound to the silane coupling agent is 3:1.

The nitrogen-free oxidant is sodium chlorate.

The average particle size of the zirconium sol is 10 nm.

The model of the zirconium sol is HN-RJ80, which was purchased from Hangzhou Hengge Nanotechnology Co., Ltd.

The average particle size of the titanium sol is 10 nm.

The model of the titanium sol is HN-TA33, which was purchased from Hangzhou Hengna New Materials Co., Ltd.

The mass ratio of the silane coupling agent, the zirconium sol and the titanium sol is 18:1:1.

The complexing agent is potassium sodium tartrate.

The rare earth compound is lanthanum chloride.

The third aspect of this embodiment provides an application of a phosphorus-free and nitrogen-free pre-painting conversion agent, which is applied to the surface treatment of aluminum alloys before painting.

Comparative Example 1

The specific implementation of Comparative Example 1 is the same as that of Example 1, except that there is no nano-dispersion liquid in the raw materials.

Comparative Example 2

The specific implementation of Comparative Example 2 is the same as that of Example 1, except that, by mass percentage, the raw material contains 4% of fluorine ion compound and 1.5% of silane coupling agent.

The fluoride ion compound is fluorotitanic acid and potassium fluorozirconate, and the mass ratio thereof is 4:1.

The fluorotitanic acid is a fluorotitanic acid aqueous solution with a mass concentration of 50%.

The aqueous solution of fluorotitanic acid with a mass concentration of 50% is from Zhonghe Chemical (Shandong) Co., Ltd.

The silane coupling agent is an epoxy silane oligomer.

The epoxysilane oligomer was purchased from Guangzhou Zhongjie New Materials Co., Ltd., model number 8066.

Comparative Example 3

The specific implementation of Comparative Example 3 is the same as that of Example 1, except that the nitrogen-free oxidant is persulfate.

The persulfate is sodium persulfate.

The sodium persulfate was purchased from Jinan Jinhao Chemical Co., Ltd.

Comparative Example 4

The specific implementation of Comparative Example 4 is the same as that of Example 1, except that, by mass percentage, the raw materials do not contain a silane coupling agent, the zirconium sol is 0.1%, and the titanium sol is 0.1%.

The average particle size of the zirconium sol is 10 nm.

The model of the zirconium sol is HN-RJ80, which was purchased from Hangzhou Hengge Nanotechnology Co., Ltd.

The average particle size of the titanium sol is 10 nm.

The model of the titanium sol is HN-TA33, which was purchased from Hangzhou Hengna New Materials Co., Ltd.

Comparative Example 5

The specific implementation of Comparative Example 5 is the same as that of Example 1, except that the complexing agent is triethanolamine.

Performance Effects

The solutions of Examples 1 to 3 and Comparative Examples 1 to 5 were diluted 100 times by mass with deionized water, and the pH value was adjusted to 3.8 with sodium hydroxide (the solution with a high pH value was adjusted to 3.8 with sulfuric acid) to form a working solution. The degreased cold-rolled steel sheet was immersed in the working solution, reacted at 25° C. for 3 minutes, rinsed with clean deionized water and dried to form a nano-scale inorganic film.

1. According to the method specified in GB/T 1740-2007, a wet heat test was performed on the cold rolled steel sheets treated with the diluted working solutions of Examples 1 to 3 and Comparative Examples 1 to 5 to test their anti-rust performance, and the maximum time without rust was recorded. The results are shown in Table 1.

2. Electrostatically spray epoxy-polyester mixed powder coating (coating thickness 70-80μm) on the treated cold-rolled steel plate, and conduct neutral salt spray test (NASS test) according to the requirements of GB/T1771. At the end of the test, the corrosion expansion at the scratch is no more than 2mm. Record the test time when the corrosion expansion reaches 2mm. The results are shown in Table 1.

3. Observation was performed on the cold-rolled steel sheets treated with the diluted working solutions of Examples 1 to 3 and Comparative Examples 1 to 5.

4. Test the adhesion according to the requirements of GB/T9286 and record the results in Table 1

Table 1

Claims (10)

1. A phosphorus-free and nitrogen-free pre-coating conversion agent, characterized in that the raw materials for its preparation, by mass percentage, are 3-15% of fluorine ion compound, 0.02-1% of nano-dispersion liquid, 0.01-1% of low-carbon alcohol, 1-5% of silane coupling agent, 0.1-2% of nitrogen-free oxidant, 0.01-0.5% of zirconium sol, 0.01-0.5% of titanium sol, 0.1-0.5% of complexing agent, 0.15-0.3% of rare earth compound, and the balance is deionized water. 2. The phosphorus-free and nitrogen-free pre-coating conversion agent according to claim 1, characterized in that the fluoride ion compound comprises one or more of fluorozirconic acid, fluorotitanic acid, potassium fluorozirconate, sodium fluorozirconate, potassium fluorotitanate, and sodium fluorozirconate. 3. The phosphorus-free and nitrogen-free pre-coating conversion agent according to claim 1, characterized in that the nano-dispersion liquid comprises one or more of γ-phase alumina, fumed silica, nano-barium sulfate, and nano-calcium carbonate. 4. The phosphorus-free and nitrogen-free pre-painting conversion agent according to claim 1, characterized in that the low-carbon alcohol includes one or more of methanol, ethanol, and isopropanol. 5. The phosphorus-free and nitrogen-free pre-coating conversion agent according to claim 1, characterized in that the silane coupling agent includes one or more of γ-(2,3-epoxypropyloxy)propyltrimethoxysilane, epoxysilane oligomer, 1,2-bis(triethoxysilyl)ethane, 3-chloropropyltriethoxysilane, 3-mercaptopropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, and vinyltrimethoxysilane. 6. The phosphorus-free and nitrogen-free pre-coating conversion agent according to claim 1 is characterized in that the nitrogen-free oxidant includes one or more of sodium molybdate, sodium tungstate, sodium chlorate, sodium bromate, and persulfate. 7. The phosphorus-free and nitrogen-free pre-painting conversion agent according to claim 1 is characterized in that the complexing agent is one or more of trisodium citrate, potassium sodium tartrate, tannic acid, sodium gluconate, lactic acid, and itaconic acid. 8. A method for preparing a phosphorus-free and nitrogen-free pre-coating conversion agent according to any one of claims 1 to 7, characterized in that it comprises the following steps: S1: adding the nano-dispersant to 5% of the deionized water of the raw material, stirring and shearing at high speed at 20-25° C. for 30-120 min to obtain a nano-dispersed liquid; S2: dissolving low-carbon alcohol into 5% deionized water of the raw material, slowly adding silane coupling agent, stirring thoroughly at 30-50° C. for 2-6 hours, slowly adding zirconium sol and titanium sol, stirring evenly, and standing for 24 hours to obtain a silane-zirconium-titanium pre-hydrolyzed copolymer; S3: Dissolve the fluoride ion compound, nitrogen-free oxidant, complexing agent and rare earth compound in the remaining amount of deionized water, add the nano-dispersion liquid and silane-zirconium-titanium pre-hydrolyzed copolymer respectively, and stir evenly. 9. Use of the phosphorus-free and nitrogen-free pre-painting conversion agent according to any one of claims 1 to 7, characterized in that it is used for surface treatment of steel and aluminum alloy before painting. 10. The use of the phosphorus-free and nitrogen-free pre-painting conversion agent according to claim 9, characterized in that the method of application is: use after degreasing and water washing; during the water washing process, 0.1-2% nitrogen-free oxidant is added.